Thermal management remains a significant challenge in set top boxes. With the introduction of more components such as smart card readers and increased functionalities, which tend to produce more heat, the need for an improved thermal management system exists.
An additional complication in set top boxes is the need to reduce the size of set top boxes due to consumer preference. This trend for compactness also makes thermal management a challenge, because this greater compactness with an increase in the number of internal components generally results in a concentration of heat.
Proper thermal contact between a thermal pad on a circuit board and a heat sink improves heat dissipation from the circuit board. Existing means for securing the heat sink against the thermal pad result in undesirable rattling of the heat sink against the thermal pad and set top box. Additionally, existing securing means do not provide sufficient contact of the thermal pad with the heat sink.
Therefore, a need exists for a retainer to secure a heat sink in proper contact with the thermal pad and stabilize the heat sink to reduce rattling.
FIGS. 1-9 illustrate a set top box that employs one means of ensure thermal contact and heat sink stabilization. The shortcomings of the system in FIGS. 1-9 is that it is preferable to have long grooves formed in the heat sink and it may be necessary for some additional means to be added to the base to secure the hold down.
However, the disclosed invention can be utilized with all of the embodiments or some of the embodiments shown and described in FIGS. 1-9. It can be used with the features used without the hold down and with the additional means added to the base or it can be used with the hold down and without the additional means.
As illustrated in FIG. 1, a circuit board 5 is housed within a top cover 7 of a set top box 1. A thermal barrier 4 is positioned between the circuit board 5 and a bottom frame 2. A smart card reader 3 is connected to the circuit board 5 through an aperture 8 in the thermal barrier 4. The set top box 1 has internal components including the smart card reader 3, the thermal barrier 4, the circuit board 5, and a heat sink 6 that contacts the circuit board 5 and is positioned between the bottom frame 2 and the top cover 7. The thermal barrier 4 includes a thermal insulating material that preferably has substantially the same profile as the circuit board 5 or a profile that is at least 80% of the area profile of the circuit board 5. The thermal barrier 4 keeps the smart card reader 3 and other components under the circuit board 5 from overheating, in part, by preventing heat from transferring from the circuit board 5 and the components thereon.
The heat sink 6 is a heat dissipating feature that removes heat from the circuit board 5. The heat sink 6 has a top plan profile that completely covers the circuit board 5 or substantially covers the circuit board 5 such that at least 80% of the circuit board 5 is covered. The heat sink 6 may include a thermal pad 9. Referring now to FIG. 3, the heat sink 6 is a contoured plate that has a generally planar periphery 52 and a recessed feature such as a central depression 53 into a plane of the planar periphery 52, wherein the planar periphery 52 preferably surrounds the central depression 53. The central depression 53 has side walls extending from the planar periphery 52 and forming an obtuse angle therewith. The central depression 53 has a flat bottom that is designed to contact the circuit board 5, the heat generating components on the circuit board 5, and/or the thermal pad 9.
Referring now to FIGS. 2 and 3, the heat sink 6 has vertical extensions 64 at the outer edges of the planar periphery 52 that are perpendicular to the planar periphery 52 and that extend over the circuit board 5 and contact the bottom frame 2 or vertically extending portions 62 of the bottom frame 2. The heat sink 6 attaches to the bottom frame 2 through slots and clips formed on these elements. The vertically extending portions 62 extend from the bottom frame 2 and have receiving slots 61 that are designed to receive clips 71 formed on the vertical extensions 64 of the heat sink 6. The vertically extending portions 62 may be plastic components, and as such, allow the heat sink clips 71 to elastically snap into the slots 61, thereby securing the heat sink 6 to the bottom frame 2. As illustrated in FIG. 2, the arrow indicates how the heat sink clips 71 are pressed downward into the bottom frame slots 61.
FIG. 3 is a perspective view of interior components of the set top box 1. The set top box 1 may include a second central depression 90 that contacts a secondary thermal pad 99 (not shown) associated with the smart card reader 3. The bottom frame 2 may include a smart card access slot 91 below the circuit board 5 and one of the vertical extensions 64 of the heat sink 6. The slot 91 may also be between the vertically extending portions 62 of the bottom frame 2. The second central depression 90 thermally communicates with the smart card reader 3 through an aperture 8 in the circuit board 5 or the secondary thermal pad 99 through the circuit board 5.
The set top box 1 described in FIGS. 1-3 further includes a hold down 130 to secure the heat sink 6 against the circuit board 5. FIG. 4 shows an exploded view of the set top box 1 with the hold down 130. The hold down 130 includes a frame that defines a perimeter. The hold down 130 may be a rectangular frame that generally matches the shape of the heat sink 6. The perimeter of the hold down 130 includes retainers 103 arranged at the ends of the hold down 130. The retainers 103 are shaped to match and engage mating locations provided on at least the bottom frame 2. The heat sink 6 may also include mating locations for the retainers 103. The hold down 130 is preferably constructed from a rigid flexible material, such as a wire or multiple wires, preferably stainless steel, that may extend diagonally to bias the heat sink 6 downwards against the thermal pad 9 and to provide contact between the circuit board 5, the thermal pad 9, and the central depression 53 of the heat sink 6 for proper thermal dissipation. The wires may cross each other such that one wire includes a bent portion that extends below the other wire. The region where the hold down components or wires cross can be centralized to be over the central depression and can be inside the central depression. The hold down or wires can be applied to the prior art assemblies to enhance heat transfer to the heat sink.
The bottom surface of the central depression 53 and the circuit board 5 contact the thermal pad 9 on opposite sides and sandwich the thermal pad 9 between them. The hold down 130 improves the surface contact among these components.
The hold down 130 may be formed from a resilient material. The hold down 130 is preferably dimensioned such that the hold down 130 is tensioned when installed and exerts a biasing force across the top of the heat sink 6 or at a specific location on the heat sink 6 after the retainers 103 of the hold down 130 engage the mating locations of the bottom frame 2 and the heat sink 6.
The top surface of the heat sink 6 may define a longitudinal plane and the frame of the hold down 130 may extend in this plane or in a parallel plane. As shown in FIG. 9, when the hold down 130 engages the mating locations of the bottom frame 2 and the heat sink 6 and the hold down 130 engages the top surface of the heat sink 6, the heat sink 6 and the hold down 130 bows in the downward direction away from the initial plane or planes. The hold down 130 may also include end portions that rise vertically above the longitudinal plane of the heat sink 6. The extent of the hold down 130 between the end portions may bow downwardly to apply force to the heat sink 6. The hold down 130 may include a central portion that extends downward into the central depression 53 of the heat sink 6 and along the inner contours of the central depression 53 such that the hold down 130 is in further contact with the heat sink 6 and movement is further reduced. As compared to existing set top boxes, the hold down 130 allows for a thinner thermal pad 9 to be used because of the biasing force from the hold down 130 on the heat sink 6.
FIGS. 5-8 show various features of the set top box 1 and the hold down 130. The retainers 103 of the hold down 130 engage slots 92 formed on the vertically extending portions 62 of the bottom frame 2 and slots 120 formed on the vertical extensions 64 of the heat sink 6. FIG. 5 shows an assembled cutaway view of the set 5 top box 1 with the hold down 130 pressing the central depression 53 of the heat sink 6 downward onto the thermal pad 9 on the circuit board 5. The heat sink 6 may include grooves 67 that are sufficiently deep to receive the hold down 130 and prevent the hold down 130 from protruding above the heat sink 6. The grooves 67 allow the vertical height of the set top box 1 to remain the same as compared to set top boxes without a hold down. The vertical extensions 64 of the heat sink 6 may also include cut out portions 140 that are shaped to receive retainer portions 103 of the hold down 130.
FIG. 6 is sectional side view of the set top box 1 and illustrates the improved contact of the bottom surface of the central depression 53 with the thermal pad 9 as compared to existing set top boxes. FIG. 7 illustrates the slots 61 on the bottom frame 2 for receiving the clips 71 of the heat sink 6, and the slots 92 for receiving the retainers 103 at the ends of the hold down 130. FIG. 8 shows alternative embodiments of the retainers 103 of the hold down 130 and illustrates the retainers 103 may include any suitable end which secures the hold down 130 with the mating locations of the bottom frame 2 and the heat sink 6. The retainers 103 may include ends 132 with U-shaped or V-shaped inward contours that engage the slots 92 of the bottom frame 2 and the slots 120 of the heat sink 6. The retainers 103 may alternatively include ends 134 with a first vertical portion, a lower horizontal portion, and second vertical portion which engage the slots 92, 120 of the bottom frame 2 and heat sink 6. As noted above, the ends 132, 134 may engage the slots 92, 120 in such a way to tension the hold down 130.